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Grade 8Metals and Nonmetals


Extraction of metals from ores


Metals are incredibly important to our daily lives; they form the basis of our transportation, construction, manufacturing, and many other industries. However, these metals are not just found in usable form; most of them are extracted from minerals found in the Earth's crust. In this comprehensive guide, we will explore the processes of extracting metals from ores, focusing on the processes that go into them, and the principles behind these methods.

What are ores?

An ore is a naturally occurring substance or rock that contains a metallic compound from which the metal can be extracted economically and profitably. Ores often contain unwanted substances, collectively called gangue. In order to use the metal, the ores must be processed to separate the metal into a form we can use.

Example 1: Bauxite is an ore from which aluminum is extracted. It consists mainly of aluminum oxide (Al 2 O 3). Other elements in bauxite include iron oxide and clay minerals.

Stages of metal extraction from ores

The extraction of metals from ores involves several major stages:

  1. Mined from the earth.
  2. It is crushed and ground to free the metallic mineral from the surrounding gangue.
  3. Concentration process to remove unwanted materials.
  4. Reduction process to extract pure metal.

Mental mining techniques

Mining is done using a variety of methods, but depending on the depth of the ore, it can generally be classified into two types:

1. Surface mining

Surface mining, also known as open-pit mining, involves removing surface vegetation, soil, and possibly bedrock layers to access buried ore deposits. This method is cost-efficient for shallow deposits.

Example 2: Iron ore is often mined through surface mining techniques due to its large quantity and relatively shallow depth.

2. Underground mining

Underground mining is used for deeper ore deposits, which requires more manpower and also costs more because of the necessary infrastructure, ventilation and safety measures.

Example 3: Precious metals such as gold and platinum are often extracted through underground mining.

Crushing and grinding

Once the ore is mined, it must undergo further processing in the form of crushing and grinding to break the rock containing the ore into smaller, more manageable pieces. This increases the surface area of the ore, making it easier to extract the metal inside it.

Concentration of ore

Concentration of ore involves washing away unwanted substances (gange) from the metal ore. It often involves a combination of different physical processes:

Physical processes

  • Gravity separation: uses the density difference between the ore and waste.
  • Magnetic separation: Uses the magnetic properties of the metal, if applicable.
  • Froth flotation: Uses differences in surface properties to separate valuable minerals from waste materials.
Example 4: Froth flotation in copper mining. Finely ground ore is mixed with water to form a slurry, air is blown into the mixture, and the copper minerals cling to the bubbles and float to the surface.

Reduction: Extraction of pure metal

Reduction is the final step, where the metal compound is reduced to the actual metal. Three primary techniques are used:

Chemical reduction

It involves using reducing agents such as carbon (in the form of coke), hydrogen or aluminium to reduce the metal compound to its metallic form. A classic example of this method is blast furnace operation.

        Fe 2 O 3 + 3C → 2Fe + 3CO
    

Here, iron(III) oxide is reduced to iron using carbon as the reducing agent.

Electrolytic reduction

In this process, electricity is used to bring about reduction. Metals such as aluminium and sodium are extracted using this technique, which are divided into two categories:

  • Electrolysis of molten compounds: Used in the extraction of very reactive metals.
  • Electrolysis of aqueous solutions: for metals that can be deposited from water-based solutions.
        2Al 2 O 3 + 3C → 4Al + 3CO 2
    

Aluminium is produced from bauxite ore and chrysolite by electrolytic reduction.

Roasting and baking

These thermal processes are used depending upon the chemical nature of the metal ore:

Roast

This involves heating the ore in the presence of oxygen, where applicable, to remove volatile impurities. Sulfide ores such as zinc and lead often undergo a process called roasting.

        2ZnS + 3O 2 → 2ZnO + 2SO 2
    

Cook

Calcination involves heating the ore in the absence or limited supply of oxygen, which helps remove moisture and volatile substances. In this process carbonates are often converted to oxides.

        CaCO 3 → CaO + CO 2
    

Metallurgical methods used for different metals

Specific methods have been adopted for the extraction of each metal depending on its source, physical and chemical properties and cost-effectiveness.

  • Iron: Blast furnace method for extraction from iron ore.
  • Aluminium: Electrolysis of Bauxite Ore.
  • Copper: Froth flotation followed by roasting and then electrolysis.

Visualization of metal extraction

To understand these processes, imagine a company working on a mountain of ore. Initially, machines and workers remove the topsoil and vegetation, revealing the heavy deposits beneath the surface. Large trucks transport these rocks to a processing facility, where the rocks are crushed into smaller pieces. Next, the crushed ore is washed, filtered, and finally subjected to heat to obtain the pure metal.

Mining Ore Processing

As we have explained, extracting metals from ores is a multi-step process that involves a combination of mechanical, chemical, and sometimes electrical means to obtain pure metals. Though often complex, understanding the extraction process is important in understanding how raw materials are transformed into the metals that are fundamental to modern civilization.


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